Ultrasonically created fluid effects have been noted in the literature since the early 1900's. Since the 1960's, the development of improved transducers for generating ultrasonic energy increased activity in this field. Ultrasonic phenomena which relate to fluid processing or coating technologies include cavitation, viscous heating, increased shear, microturbulence, and acoustic streaming. These phenomena generate effects that include enhanced wettability, micromixing, dispersion, emulsification, deaeration, agglomeration, separation of components, viscosity reduction, polymer chain disentanglement, high polymer degradation, and increased chemical reaction rates.
Last, et al., U.S. Pat. No. 4,302,485, discloses using ultrasonic energy in an immersed saturation system to excite a strip of fabric passing through a bath of liquid finishing agent. This causes cavitation in the bath and increases the microturbulence to thereby increase wicking. The fabric is impregnated from both sides, and the liquid is not metered onto the fabric.
In U.S. Pat. No. 4,307,128 to Nagano, et al., ultrasonic energy is used in a molten metal bath to locally lift a portion of the molten metal surface such that it contacts a moving surface of a substrate. The coating is not metered. Absent ultrasonic energy, this apparatus is apparently inoperative.
U.S. Pat. No. 3,676,216 to Abitboul teaches applying ultrasonic energy to a previously coated web to more uniformly and consistently distribute the coating over the web and to smooth irregularities in the coating. However, the ultrasonic energy is transmitted through the air to excite the coated web after the web is completely coated.
Japanese Patent No. 57-187071 discloses applying ultrasonic energy to the backside of a coated web. However, the ultrasonic source is too far from the point of coating for the ultrasonic energy to affect the liquid at the first contact between the liquid and the web or at the last contact between the liquid and the coating equipment.
In Canadian Patent No. 869,959, a nozzle for applying a liquid coating from a hopper onto a moving web is ultrasonically excited. A horn ultrasonically vibrates the nozzle to prevent the coating from sticking in and clogging the nozzle. However, the ultrasonic vibrations only affect the coating before it is placed on the web, and do not affect the process during the initial contact between the coating and the web or thereafter. Thus, the ultrasonic vibrations do not affect the uniformity of the thickness of the coating as the coating is applied. The Canadian patent is representative of a body of art which discloses applying ultrasonic energy to a nozzle during coating to improve flow through and from the nozzle. However, these apparatus are not practical for use in large scale production applications where wide coatings are being applied. In the formation of web rolls such as adhesive tapes, it is common to form the rolls in up to 150 cm (60 inch) widths. Rolls this size could not be formed while achieving uniform ultrasonic excitation of sufficient intensity at the nozzle due to the difficulty in exciting the necessary masses and lengths involved.
None of the known apparatus or systems disclose metering the coating onto only one side of the web and using acoustic energy to improve the characteristics of an applied coating before the coating of the web is complete.